Question

On adding $\text{N}{{\text{H}}_{\text{4}}}\text{OH}$ to $\text{MnC}{{\text{l}}_{\text{2}}}$, the precipitate formed is:
A.$\text{N}{{\text{H}}_{\text{4}}}\text{Cl}$
B.$\text{Mn}{{\left( \text{OH} \right)}_{\text{2}}}$
C.No precipitate
D.Both A and B

Answer 1

Precipitation occurs in a chemical reaction when cations and anions in a solution combine to form an insoluble ionic solid called the precipitate. Whether or not there will be precipitation in a chemical reaction is determined from the solubility product of the products formed in the medium.

Complete answer:
When ammonium hydroxide is added to the manganese chloride solution, it results in the formation of manganese hydroxide and ammonium chloride. The manganese hydroxide initially precipitates out as a white coloured precipitate but then dissolves in the presence of ammonium chloride to give a clear colourless solution. Hence, excess ammonia does not dissolve the manganese hydroxide precipitate but the ammonium chloride does and hence the answer would be that there is no precipitation on the addition of ammonium hydroxide to manganese chloride.

So, the correct option is C, “no precipitate”.
Note:
Manganese chloride or any other manganese salt solution precipitates out as manganese hydroxide on the addition of sodium hydroxide to the salt solution. The white coloured precipitate slowly turns yellowish brown on the oxidation of Manganese by atmospheric oxygen to form$\text{Mn }\left( \text{III} \right)$ or $\text{Mn }\left( \text{IV} \right)$.
In basic solutions, hydrogen peroxide oxidises $\text{Mn }\left( \text{II} \right)$ to $\text{Mn }\left( \text{IV} \right)$ giving a brown precipitate of manganese dioxide. Hence hydrogen peroxide acts as an oxidising agent in this reaction. The manganese dioxide formed as a result of oxidation is generally insoluble in acids but it dissolves in concentrated hydrochloric acid to release oxygen gas.